Process and formulation for producing a polyamide having low caprolactam concentration and specific relative viscosity

ABSTRACT

A base polyamide composition comprising a nylon mixture having caprolactam units from 1 wppb to 50 wppm catalyst composition; and greater than 0.75 wt % residual caprolactam, wherein the base polyamide composition has a delta end group level ranging from 30 neq/gram to 90 neq/gram.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to and filing benefit of U.S.Provisional Patent Application No. 62/721,259, filed on Aug. 22, 2018,which is incorporated herein by reference in its entirety.

FIELD

The present disclosure relates generally to polyamide formulations andto processes for producing polyamides. More specifically, the presentdisclosure relates to processes for producing polyamides using a solidstate polymerization step which yields a polyamide composition having alow residual caprolactam concentration and/or a preferred relativeviscosity.

BACKGROUND

Nylon-6; nylon-6,6; and various copolymers thereof have been widely usedin various applications, e.g., film formation, extrusion, (injection)molding, fiber, and food packaging films, because of their advantageousproperties. These polymers/copolymers are formed via a polymerizationreaction, as is well known.

In some cases, the caprolactam monomers used in the polymerizationreaction to form the polymers/copolymers may not entirely polymerizeinto high molecular caprolactam monomers and oligomers. This residualcaprolactam must then be removed because, among others, it contributesto production inefficiencies such as plate out on equipment, e.g., dies;presents problems relating to industry limits for food contactapplications, and presents an unpleasant volatile odor. In conventionalprocesses, residual caprolactam may be removed by extraction with hotwater. The monomeric caprolactam in the extraction water can be purifiedand cleaned to recapture caprolactam, which can be recycled to thepolymerization reactor. It is also possible to react the oligomersobtained in the extraction water back into caprolactam monomers byadding splitting reagents then isolating and washing to yield themonomers, which may then be reused. Also, U.S. Pat. No. 4,053,457discloses a process for the manufacture of polyamides from ε-caprolactamand/or other polyamide-forming starting compounds by polymerization andsubsequent extraction of the polymer. The extract containing solvent,monomer, and oligomers is concentrated in the absence of atmosphericoxygen. The surfaces that come into contact with the extract are made ofmaterials that are inert under the conditions of the concentrationprocess. The resultant concentrate, without further purification orseparation, is polymerized by itself or together with otherpolyamide-forming starting compounds.

In many of these situations, it is desirable for the finalpolymer/copolymer (collectively polymer(s)) to exhibit higher relativeviscosity (RV), molecular weight, (in combination with lower volatile,e.g., residual caprolactam, concentration). Molecular weight may beincreased by utilizing a solid phase polymerization (SSP)process/operation, which is preferably employed after the crude polymeris polymerized and washed. As one example, SSP may be carried out bypassing a hot inert gas flow through a heated bed of polymerpellets/granules. As another example, U.S. Pat. No. 6,069,228 disclosesa process for preparing polyamide polymers via prepolymer formation in areactor system comprising a reactor, flasher and separator,crystallization of the prepolymer under controlled temperatureconditions and the subsequent conversion of these crystallizedprepolymers to high molecular weight polymer via SSP. Also, U.S. Pat.No. 6,476,181 discloses a process for increasing the molecular weight ofnylon 6 while reducing its content of caprolactam and other volatiles bya two-staged heating process.

The compositional and performance properties of the polymer, e.g.,polyamide, are often in conflict with one another, and processing toachieve a low caprolactam concentration may have an adverse effect onmolecular weight or RV build, among others. As one example ifcaprolactam removal requires more SSP time than does the molecularweight increase, then the resultant molecular weight will build for toolong and will be excessively high at the end of the SSP operation. Insome cases, the build rate of the RV and/or the molecular weight overtime has a non-linear profile, which leads to control problems.Generally speaking, conventional polymer products have been unable toachieve low caprolactam concentration in combination with desirablemolecular weight and/or relative viscosity, especially where the initialpre-SSP polymer has a high molecular weight and a high caprolactamconcentration.

In addition to the challenges related to the compositional andperformance properties, the overall pellet quality of conventionalpolyamide compositions has been found to be adversely affected by theSSP process.

An advantage of Nylon-6,6, aside from higher thermal performance, is itscleanliness. In contrast, use of other polymers has been found to resultin thermal reversibility, thereby resulting in even more residualcaprolactam monomer, see M. Kohan, Nylon Plastics Handbook, 1995. Thisissue is especially germane in film-related applications. This outcomeis undesirable as extractable monomer levels are known to adverselycompromise safeness and approvals for food contact applications, seeFood and Drug Administration, HHS, 21 CFR Ch. I, 4-1-02 Edition, 2002.

Even in view of the references, the need exists for a base polyamidecomposition that is capable of forming, preferably via an SSPprocess/operation, final polyamide compositions having a low residualcaprolactam concentrations, desirable final RVs, and other beneficialpellet-related properties.

All of the references discussed herein are hereby incorporated byreference.

SUMMARY

In some embodiments, this disclosure relates to a process for producinga polyamide composition having a low residual caprolactam concentration,the process comprising the steps of providing a base polyamidecomposition and processing the base polyamide composition to form thefinal polyamide composition. The base polyamide composition may comprisea nylon mixture having caprolactam units, e.g., greater than 1.4 wt %caprolactam units; from 1 wppb to 50 wppm of a catalyst composition; andresidual caprolactam, and may have a melting point ranging from 180° C.to 255° C. The base polyamide composition may have an initial residualcaprolactam concentration, e.g. greater than 0.75 wt %, an initialrelative viscosity, e.g., less than 55, and a delta end group levelranging from 30 μeq/gram to 90 μeq/gram and/or a delta end group levelgreater than 50 μeq/gram. The nylon mixture may comprise from 1 wt % to80 wt % nylon-6 and from 20 wt % to 99 wt % nylon-6/6. The basepolyamide composition may be produced by melt polymerizing a polyamidecomposition and pelletizing the melted polyamide composition to formpolyamide pellets. In some cases, the catalyst composition comprisesphosphorous acid; phosphonic acid; alkyl- and aryl-substitutedphosphonic acids; 2-pyridylethyl phosphonic acid; hypophosphorous acid;alkyl-, aryl- and alkyl-/aryl-substituted phosphinic acids; phosphoricacid; esters and salts of these phosphorous-containing acids; manganesehypophosphite; sodium hypophosphite; benzene phosphinic acid; ormonosodium phosphate; or any combinations thereof. The final polyamidecomposition may have a final residual caprolactam concentration, e.g.,less than 0.75 wt %, a final relative viscosity, e.g., ranging from 40to 350, and/or a color index ranging from −6 to 5. The final relativeviscosity may be greater than the initial relative viscosity, e.g., atleast 10% greater than the initial relative viscosity and the finalresidual caprolactam concentration is at least 5% less than the initialresidual caprolactam concentration. During processing, the initialrelative viscosity may increase at a build rate that is substantiallylinear. In some cases, the processing comprises solid statepolymerization, which may comprise heating the base polyamide. Theprocessing may be conducted for a build time less than 30 hours, andoptionally at a temperature ranging from 150° C. to 250° C., e.g., from170° C.-190° C. and optionally at a pressure less than atmosphericpressure. The final polyamide composition may comprise less than 10 wt %tinting agent and/or the base polyamide composition may comprise lessthan 10 wt % tinting agent. In one embodiment, the base polyamidecomposition comprises from 0.1 wppm to 30 wppm catalyst composition,from 1 wt % to 8 wt % residual caprolactam and has a delta end grouplevel ranging from 50 μeq/gram to 75 μeq/gram and has initial relativeviscosity less than 35 and wherein the final polyamide compositioncomprises less than 0.5 wt % residual caprolactam and has a finalrelative viscosity greater than 45. In one embodiment, the basepolyamide composition comprises from 1 wppb to 35 wppm phosphorus,greater than 1.5 wt % caprolactam and has a delta end group levelgreater than 50 μeq/gram and has initial relative viscosity less than 33and wherein the processing is conducted at a pressure less thanatmospheric pressure and a temperature ranging from 175° C. to 185° C.,and wherein the final polyamide composition comprises less than 0.4 wt %residual caprolactam and has a final relative viscosity greater than 55,e.g., greater than 75.

In some embodiments, the disclosure relates to a process for producing apolyamides having a low residual caprolactam concentration, the processcomprising the steps of providing the base polyamide composition andprocessing the base polyamide composition to form a final polyamidecomposition.

In some embodiments, the disclosure relates to a film formed from afinal polyamide composition. The film may demonstrate a punctureresistance greater than 3 J/mm, an impact resistance greater than 1500grams, and/or a tear resistance greater than 50 grams.

In some embodiments, the disclosure relates to a process for controllingthe relative viscosity of a final polyamide composition, the processcomprising the steps of providing a base polyamide composition havingrelative viscosity less than 40; determining a desired relativeviscosity for the final polyamide composition; selecting at least oneprocessing condition from catalyst content, delta end group level,temperature, pressure, and moisture content; and processing the basepolyamide composition under the at least one processing condition andbased on the desired relative viscosity to form the final polyamidecomposition having a final relative viscosity ranging from 55 to 200,e.g., from 75 to 200.

In some cases, the disclosure relates to a process for controlling thecaprolactam content of a final polyamide composition, the processcomprising the steps of providing a base polyamide composition havingresidual caprolactam content greater than 0.6 wt %; determining adesired residual caprolactam content for the final polyamidecomposition; selecting at least one processing condition from catalystcontent, delta end group level, temperature, pressure, and moisturecontent; and processing the base polyamide composition under the atleast one condition and based on the desired residual caprolactamcontent to form the final polyamide composition having a residualcaprolactam content less than 0.4 wt %.

In one embodiment, the disclosure relates to a process for manufacturinga final polyamide composition, the process comprising the steps ofproviding a base polyamide composition having one or more initialproperties comprising initial caprolactam content, initial relativeviscosity, and initial color index; determining one or more desiredfinal properties for the final polyamide composition product, theproperties comprising final caprolactam content, final relativeviscosity, and color index; and processing the base polyamidecomposition under one or more process conditions comprising catalystcontent, delta end group level, temperature, pressure, and moisturecontent and based on the desired final property to provide the finalpolyamide composition.

In some embodiments, the present disclosure relates to a process forproducing a polyamide composition having a low residual caprolactamconcentration, the process comprising the steps of: (a) providing a basepolyamide composition comprising: a nylon mixture having caprolactamunits; from 1 wppb to 50 wppm of a catalyst composition; and residualcaprolactam, and having an initial residual caprolactam concentrationand an initial relative viscosity; (b) processing the base polyamidecomposition to form the final polyamide composition having a finalresidual caprolactam concentration and a final relative viscosity. Insome cases, the base polyamide composition has a delta end group levelranging from 30 μeq/gram to 90 μeq/gram. In some cases, the initialresidual caprolactam concentration is greater than 0.75 wt %, based onthe total weight of the base polyamide composition, and the finalresidual caprolactam concentration is less than 0.75 wt %, based on thetotal weight of the final polyamide composition. In some cases, thefinal relative viscosity ranges from 40 to 350. In some cases, theprocessing is conducted for a build time ranging from 2 hours to 30hours, and a temperature ranging from 150° C.-250° C. In some cases, thefinal polyamide composition has a color index ranging from −6 to 5, asmeasured by ASTM E313 (2018). In some cases, the final relativeviscosity is greater than the initial relative viscosity, wherein thefinal relative viscosity is at least 10% greater than the initialrelative viscosity. In some cases, the base polyamide composition has amelting point ranging from 180° C. to 255° C. In some cases, the nylonmixture of the base polyamide composition comprises: from 1 wt % to 80wt % nylon-6; and from 20 wt % to 99 wt % nylon-6/6. In some cases,processing comprises solid state polymerization, which comprises heatingthe base polyamide. In some cases, the base polyamide composition isproduced by melt polymerizing a polyamide composition and pelletizingthe melted polyamide composition to form polyamide pellets. In somecases, the catalyst composition comprises phosphorous acid; phosphonicacid; alkyl- and aryl-substituted phosphonic acids; 2-pyridylethylphosphonic acid; hypophosphorous acid; alkyl-, aryl- andalkyl-/aryl-substituted phosphinic acids; phosphoric acid; esters andsalts of these phosphorous-containing acids; manganese hypophosphite;sodium hypophosphite; benzene phosphinic acid; monosodium phosphate; orany combinations thereof. In some cases, the base polyamide compositioncomprises from 0.1 wppm to 30 wppm catalyst composition, from 1 wt % to8 wt % residual caprolactam, has a delta end group level ranging from 50μeq/gram to 75 μeq/gram, and has initial relative viscosity less than35, and the final polyamide composition comprises less than 0.6 wt %residual caprolactam and has a final relative viscosity greater than 45.In some cases, the base polyamide composition comprises from 1 wppb to35 wppm phosphorus, greater than 1.5 wt % residual caprolactam, a deltaend group level greater than 50 μeq/gram and has initial relativeviscosity less than 33, wherein the processing is conducted at apressure less than atmospheric pressure and a temperature ranging from175° C. to 185° C., and wherein the final polyamide compositioncomprises less than 0.4 wt % residual caprolactam and has a finalrelative viscosity greater than 55, e.g., greater than 75. In somecases, during processing, the RV build rate ranges from 1 to 30 RVunits/hour.

In some embodiments, the present disclosure relates to a base polyamidecomposition comprising: a nylon mixture having caprolactam units; from 1wppb to 50 wppm catalyst composition; and greater than 0.75 wt %residual caprolactam; wherein the base polyamide composition has a deltaend group level ranging from 30 μeq/gram to 90 μeq/gram. In some cases,the base polyamide composition has a delta end group level greater thanor equal to 45 μeq/gram. In some cases, the base polyamide comprisesgreater than 1.4 wt % caprolactam units, based on the total weight ofthe base polyamide composition, and wherein the base polyamide has arelative viscosity less than 55. In some cases, the nylon mixture of thebase polyamide composition comprises: from 1 wt % to 50 wt % nylon-6;and from 20 wt % to 99 wt % nylon-6/6, wherein the catalyst compositioncomprises phosphorous acid; phosphonic acid; alkyl- and aryl-substitutedphosphonic acids; 2-pyridylethyl phosphonic acid; hypophosphorous acid;alkyl-, aryl- and alkyl-/aryl-substituted phosphinic acids; phosphoricacid; esters and salts of these phosphorous-containing acids; manganesehypophosphite; sodium hypophosphite; benzene phosphinic acid; monosodiumphosphate; or any combinations thereof.

In some embodiments, the present disclosure relates to a film formedfrom a final polyamide composition comprising: polyamide monomers; lessthan 0.75 wt % residual caprolactam, wherein the final polyamidecomposition has a delta end group level ranging from 30 μeq/gram to 90μeq/gram and a melting point ranging from 205° C. to 255° C. In somecases, the film demonstrates: a puncture resistance greater than 3 J/mmas measured via ASTM F1366 (2018), an impact resistance greater than1500 grams as measured via ASTM D1709. A (2018), and/or a tearresistance greater than 50 grams as measured via ASTM D1922 (2018).

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure references the appended drawings.

FIG. 1 is a graph showing residual caprolactam concentration in finalpolyamide compositions at various build times.

FIG. 2 is a contour plot showing desirable DEG and catalyst (phosphorus)concentration in base polyamide compositions.

FIG. 3 is a plot showing desirable final RV and residual caprolactam inthe base polyamide compositions of Examples 9-14.

DETAILED DESCRIPTION Introduction

Conventional processes for producing final polyamide compositions oftenemploy a polymerization step to form a base polyamide compositionfollowed by solid phase polymerization (SSP) of the base polyamide toform the final polyamide compositions. As noted above however, theseprocesses yield final polyamide compositions that have, among otherdrawbacks, high residual caprolactam concentrations and/or undesirablerelative viscosities (RVs). In addition to these compositional andperformance deficiencies, the overall pellet quality of conventionalfinal polyamide compositions has been found to be poor. For example,typical final polyamide compositions exhibit poor color quality, e.g.,high yellowing indices; high levels of black specks; and/or high degreesof pellet size non-uniformity. It is postulated that the use of the SSPprocess exacerbates the compositional shortcomings of the conventionalbase polyamide compositions and further contributes to these problems.

The inventors have now discovered base polyamide compositions comprisingspecific components and having particular properties, that, whenprocessed via SSP, provide for a final polyamide compositions thatdemonstrate beneficial combinations of features. It has been found thatthe use of a low concentrations of catalyst, optionally in combinationwith specific delta end group (DEG) levels, provides for the desirablefinal polyamide compositions. For example, the base polyamides disclosedherein may yield final polyamide compositions having an advantageouscombination of low residual caprolactam content, e.g., less than 0.75 wt%, and a desirable RV, e.g. ranging from 40 to 350, as measured via the90% formic acid method (additional ranges and limits for these featuresare disclosed herein). In contrast, conventional base polyamidecompositions, when processed via SSP, may provide for one of thesecharacteristics, but not more than one, e.g., not low caprolactamconcentration and desired RV in combination.

Without being bound by theory, the use of the disclosed base polyamidecompositions provides for a consistent, controllable RV build rateduring SSP, e.g., a substantially linear or linear build rate. Thisbuild rate provides for synergistic control of RV build and removal ofresidual caprolactam, e.g., by providing the ability to manipulate theRV-to-build time ratio. The disclosed base polyamide compositions alsoprovide the potential to effectively “tune” the process based on factorsto arrive at a preferred final composition. For example, at thecontrolled build rates, the build time can be controlled, e.g., to lessthan 30 hours. As a result, the rate of RV build and the rate ofcaprolactam removal synergize with one another. As an example, when therate of RV build ranges from 1 to 30 hours, then the caprolactam hasenough time to react or diffuse out of the polyamide composition—boththe RV target and the caprolactam removal target are achieved in similartime frames. It is postulated that the use of higher amounts ofcatalyst, e.g., at least 50 wppm, (as is conventionally done)detrimentally contributes to build rates that are too rapid, which donot allow sufficient time for caprolactam removal. With conventionalbase polyamides and SSP processes, the caprolactam removal takes toomuch or too little time and RV builds to an undesirable level or failsto build to a desirable level.

In addition, it has been found that the use of the base polyamides andSSP processes disclosed herein provide for a product having beneficialoverall pellet quality, e.g., good color quality (low yellowingindices); low levels of black specks; and/or high degrees of pellet sizeuniformity. In particular, the inventors have found that the use of thespecific amounts of catalyst has surprisingly been found to retardyellowing. Without being bound by theory, it is believed that lowercatalyst concentrations have a beneficial effect on color. For example,the related amount of hydrogen (radicals) donated by these catalysts,e.g., phosphite catalysts, may retard polymer oxidation, which leads topoor color qualities. The lower amounts of catalyst have been found tofavor catalysis versus other color-causing side reactions, e.g.,oxidation—the lower amounts of catalyst seem to demonstrate ananti-oxidizing benefit (in addition to the catalytic effects). Higheramounts of catalyst, in contrast, may provide hydrogen amounts thatresult in a build rate is too steep and/or non-linear. Thus, thedisclosed amounts of catalyst advantageously both retard oxidation andprovide for beneficial build rates (along with color-related and otherbenefits). As a result of the improved color quality, the resultantfinal polyamide compositions advantageously require little if anytinting agents, e.g., blue dyes, which are often employed inconventional polyamide compositions to offset poor color quality.

In one embodiment, a base polyamide composition is disclosed. The basepolyamide composition comprise a nylon mixture, a catalyst composition,and (at least some) residual caprolactam. The nylon mixture includessome polymers having caprolactam units (non-residual caprolactam). Insome cases, the residual caprolactam is present in the specific amountsdisclosed herein, e.g., at least 0.75 wt %, and the catalyst compositionis present in the specific amount disclosed herein, e.g., from 1 wppb to50 wppm. The base polyamide composition has an initial residualcaprolactam concentration and an initial RV, which are discussed in moredetail below. The nylon mixture, in some embodiments, comprises or hascaprolactam (nylon-6 or PA-6) units. In some embodiments, the basepolyamide composition has a specific delta end group level, e.g., a DEGlevel ranging from 35 μeq/gram to 85 μeq/gram.

In addition to the base polyamide compositions themselves, it has nowbeen discovered that the use of particular SSP parameters, inconjunction with the base polyamide compositions, provides forsurprising compositional benefits in the final polyamide composition andfor process related efficiencies. These SSP parameters and benefits arediscussed in detail below. Thus, in one embodiment, a process forproducing a polyamide having a low residual caprolactam concentration isdisclosed. The process comprises the steps of providing the basepolyamide composition and processing the base polyamide composition toform the final polyamide composition, which has a final residualcaprolactam concentration and a final RV. In addition, the combinationsof these features can beneficially be employed in a “tunable” manner toproduce a final polyamide composition having a target properties. Thetunable processes are discussed in more detail below.

Catalyst

The catalyst may vary widely, and there are many suitable catalystcompositions known in the art. As some examples, the catalystcomposition may comprise phosphorous acid; phosphonic acid; alkyl- andaryl-substituted phosphonic acids; 2-pyridylethyl phosphonic acid;hypophosphorous acid; alkyl-, aryl- and alkyl-/aryl-substitutedphosphinic acids; phosphoric acid; esters and salts of thesephosphorous-containing acids; manganese hypophosphite; sodiumhypophosphite; benzene phosphinic acid; or monosodium phosphate; or anycombination, e.g., 2 or more, thereof. Esters and salts of thesephosphorous-containing acids include, but are not limited to, alkyl,aryl and alkyl/aryl esters, metal salts, ammonium salts, and ammoniumalkyl salts.

Preferably, the catalyst composition comprises manganese hypophosphite,or sodium hypophosphite or any combination thereof. The aforementionedcatalysts are commercially available products.

As noted above, the catalyst composition is present in specific amounts,which have been found to contribute to surprising benefits. In someembodiments, the base polyamide composition comprises from 1 wppb to 50wppm catalyst composition, e.g., from 1 wppb to 40 wppm, from 1 wppb to37 wppm, from 10 wppb to 37 wppm, from 10 wppb to 35 wppm, from 0.1 wppmto 35 wppm, from 0.1 wppm to 30 wppm, from 0.1 wppm to 25 wppm, from 0.1wppm to 20 wppm, from 0.5 wppm to 15 wppm, from 0.5 wppm to 10 wppm;from 1 wppm to 20 wppm, from 2 wppm to 25 wppm, from 2 wppm to 20 wppm,from 1 wppm to 10 wppm, from 2 wppm to 15 wppm, from 3 wppm to 11 wppm,or from 4 wppm to 10 wppm. In terms of upper limits, the base polyamidecomposition may comprise less than 50 wppm catalyst composition, e.g.,less than 40 wppm, less than 35 wppm, less than 30 wppm, less than 25wppm, less than 20 wppm, less than 15 wppm, less than 12 wppm, less than11 wppm, less than 10 wppm, less than 8 wppm, less than 6 wppm, lessthan 5 wppm, less than 4 wppm, or less than 3 wppm. In terms of lowerlimits, the base polyamide composition may comprise greater than 1 wppbcatalyst composition, e.g., greater than 10 wppb, greater than 0.1 wppm,greater than 0.3 wppm, greater than 0.5 wppm, greater than 0.7 wppm,greater than 1 wppm, greater than 1.2 wppm, greater than 1.5 wppm,greater than 1.7 wppm, greater than 2 wppm, greater than 2.5 wppm,greater than 3 wppm, greater than 3.5 wppm, greater than 4 wppm, greaterthan 5 wppm, greater than 7 wppm, or greater than 10 wppm.

“Wppm” and “wppb,” as used herein, mean weight parts per million orweight parts per billion, respectively, and are based on the totalweight of the entire respective composition, e.g., the total weight ofthe entire base polyamide composition or the entire final polyamidecomposition. Likewise, weight percentages are based on the total weightof the entire respective composition.

In one embodiment, the catalyst composition comprises an inorganiccomponent, e.g., a phosphorus-containing component, such as inorganicphosphites. In these cases, the base polyamide composition comprisesfrom 1 wppb to 25 wppm phosphorus, e.g., from 1 wppb to 20 wppm, from 10wppb to 20 wppm, from 0.1 wppm to 20 wppm, from 0.5 wppm to 20 wppm,from 1 wppm to 20 wppm, from 1 wppm to 15 wppm, from 2 wppm to 15 wppm,from 3 wppm to 12 wppm, from 3 wppm to 13 wppm from 4 wppm to 20 wppm;from 4 wppm to 15 wppm, from 4 wppm to 12 wppm, from 10 wppm to 20 wppm,from 5 wppm to 15 wppm, from 5 wppm to 10 wppm, from 10 wppm to 16 wppm,or from 11 wppm to 15 wppm. In terms of upper limits, the base polyamidecomposition may comprise less than 25 wppm phosphorus, e.g., less than20 wppm, less than 18 wppm, less than 16 wppm, less than 15 wppm, lessthan 14 wppm, less than 13 wppm, less than 12 wppm, less than 11 wppm,less than 10 wppm, less than 9 wppm, less than 8 wppm, less than 7 wppm,less than 6 wppm, less than 5 wppm, less than 4 wppm, or less than 3wppm. In terms of lower limits, the base polyamide composition maycomprise greater than 1 wppb phosphorus, e.g., greater than 10 wppb,greater than 0.1 wppm, greater than 0.3 wppm, greater than 0.5 wppm,greater than 0.7 wppm, greater than 1 wppm, greater than 1.2 wppm,greater than 1.5 wppm, greater than 1.7 wppm, greater than 2 wppm,greater than 2.5 wppm, greater than 3 wppm, greater than 3.5 wppm,greater than 4 wppm, or greater than 5 wppm.

End Groups

As used herein, delta end groups (DEG or DEGs) are defined as thequantity of amine ends (—NH₂) less the quantity of carboxylic acid ends(—COOH). DEG calculation methods are well known.

As noted above, the base polyamide composition utilizes particularranges and/or limits of DEG levels. In some embodiments, the basepolyamide composition has a DEG level ranging from 30 μeq/gram to 90μeq/gram, e.g., from 35 μeq/gram to 85 μeq/gram, from 35 μeq/gram to 80μeq/gram, from 40 μeq/gram to 75 μeq/gram, from 50 μeq/gram to 75μeq/gram, from 40 μeq/gram to 70 μeq/gram, from 42 μeq/gram to 68μeq/gram, from 45 μeq/gram to 60 μeq/gram, from 45 μeq/gram to 65μeq/gram, from 47 μeq/gram to 63 μeq/gram, from 48 μeq/gram to 58μeq/gram, 50 μeq/gram to 60 μeq/gram, or from 52 μeq/gram to 57μeq/gram. In terms of upper limits, the base polyamide composition mayhave a DEG level less than 85 μeq/gram, e.g. less than 80 μeq/gram, lessthan 75 μeq/gram, less than 70 μeq/gram, less than 68 μeq/gram, lessthan 65 μeq/gram, less than 63 μeq/gram, less than 60 μeq/gram, lessthan 58 μeq/gram, less than 55 μeq/gram, less than 53 μeq/gram, or lessthan 50 μeq/gram. In terms of lower limits, the base polyamidecomposition may have a DEG level greater than 35 μeq/gram, e.g., greaterthan 40 μeq/gram, greater than 42 μeq/gram, greater than 45 μeq/gram,greater than 48 μeq/gram, greater than 50 μeq/gram, or greater than 52μeq/gram. Again, the utilization of the specific DEG levels provides forthe unexpected combination of advantageous, synergistic properties inthe final polyamide compositions. These ranges and limits may beimportant, for example, when the amine end balance may be important forsecondary operations, e.g., tie layer bonding, adhesion, or secondarychemistry considerations, e.g., reactions with epoxies.

In other applications, higher amine end content may not be desired. Forexample the amine end balance may not be important for secondaryoperations or may have an adverse impact, in which case an excess ofcarboxylic acid ends may be desired. In some embodiments, the basepolyamide composition has a DEG level ranging from −31 μeq/gram to −90μeq/gram, e.g., from −35 μeq/gram to −85 μeq/gram, from −35 μeq/gram to−80 μeq/gram, from −40 μeq/gram to −75 μeq/gram, from −50 μeq/gram to−75 μeq/gram, from −40 μeq/gram to −70 μeq/gram, from −42 μeq/gram to−68 μeq/gram, from −45 μeq/gram to −60 μeq/gram, from −45 μeq/gram to−65 μeq/gram, from −47 μeq/gram to −63 μeq/gram, from −48 μeq/gram to−58 μeq/gram, −50 μeq/gram to −60 μeq/gram, or from −52 μeq/gram to −57μeq/gram. In terms of lower limits, the base polyamide composition mayhave a DEG level greater than −85 μeq/gram, e.g. greater than −80μeq/gram, greater than −75 μeq/gram, greater than −70 μeq/gram, greaterthan −68 μeq/gram, greater than −65 μeq/gram, greater than −63 μeq/gram,greater than −60 μeq/gram, greater than −58 μeq/gram, greater than −55μeq/gram, greater than −53 μeq/gram, or greater than −50 μeq/gram. Interms of upper limits, the base polyamide composition may have a DEGlevel less than −30 μeq/gram, e.g., less than −35 μeq/gram, less than−40 μeq/gram, less than −42 μeq/gram, less than −45 μeq/gram, less than−48 μeq/gram, less than −50 μeq/gram, or less than −52 μeq/gram. Thesespecific DEG levels have also been found to provide for the unexpectedcombination of advantageous, synergistic properties in the finalpolyamide compositions.

In some cases, DEG level may be obtained/achieved/controlled bycontrolling the amount of excess hexamethylene diamine (HMD) in thepolymerization reaction mixture. HMD is believed to be more volatilethan the (di)carboxylic acids that are employed in the reaction, e.g.adipic acid. The HMD and the carboxylic acids act to balance the formula(based on the theoretical values for the end groups), and the balancebetween the two (and hence the DEG) can be adjusted to achieve desiredproperties in the polyamide compositions.

In some cases, the DEG level may be obtained/achieved/controlled via theincorporation of (mono) acids and/or (mono) amines, e.g., by “capping”some of the end structures to arrive at the desired DEG level, e.g., thedesired end group balance.

In some cases, the utilization of monofunctional end capping has beenfound to provide the surprising benefit of controlling, e.g., slowing,the rate of polymerization in the SSP process. Without being bound bytheory, it is believed that the capping (1) limits the amount ofreactive ends; and (2) limits the degree of polymerization to a finitenumber. In some cases, the more end capping that is employed, the lowerthe (maximum) molecular weight can be (at 100% conversion). Both theformer and latter may be achieved by creating high DEG systems. Themonofunctional addition will increase DEG level.

In one embodiment, the (mono) acids and/or (mono) amines areincorporated at levels ranging from 1 and 40 μeq/gram, e.g., from 1μeq/gram to 35 μeq/gram, from 3 μeq/gram to 35 μeq/gram, from 3 μeq/gramto 30 μeq/gram, from 5 μeq/gram to 30 μeq/gram, from 5 μeq/gram to 25μeq/gram, from 7 μeq/gram to 25 μeq/gram, from 7 μeq/gram to 20μeq/gram, from 10 μeq/gram to 20 μeq/gram, or from 10 μeq/gram to 15μeq/gram. In terms of upper limits, the (mono) acids and/or (mono)amines may be incorporated at levels less than 40 μeq/gram, e.g., lessthan 35 μeq/gram, less than 30 μeq/gram, less than 25 μeq/gram, lessthan 20 μeq/gram, or less than 15 μeq/gram. In terms of lower limits,the (mono) acids and/or (mono) amines may be incorporated at levelsgreater than 1 μeq/gram, e.g., greater than 3 μeq/gram, greater than 5μeq/gram, greater than 7 μeq/gram, or greater than 10 μeq/gram.

Exemplary (mono) acids include but are not limited to acetic acid,proprionic acid, butyric acid, valeric acid, hexanoic acid, octanoicacid, palmitic acid, myristic acid, decanoic acid, undecanoic acid,dodecanoic acid, oleic acid, or stearic acid, or any combinationsthereof. Exemplary (mono) amines include but are not limited tobenzylamine, ethylamine, propylamine, butylamine, pentylamine,hexylamine, 2-ethyl-1-hexylamine, heptylamine, octylamine, nonylamine,decylamine, undecylamine, dodecylamine, amylamine, tert-butyl amine,tetradecylamine, hexadecylamine, or octadecylamine, or any combinationsthereof.

Nylon Mixture

The nylon mixture may vary widely. In some embodiments, the nylonmixture may comprise PA-6, PA-6,6, PA4,6, PA-6,9, PA-6,10, PA-6,12,PA11, PA12, PA9,10, PA9,12, PA9,13, PA9,14, PA9,15, PA-6,16, PA9,36,PA10,10, PA10,12, PA10,13, PA10,14, PA12,10, PA12,12, PA12,13, PA12,14,PA-6,14, PA-6,13, PA-6,15, PA-6,16, PA-6,13, PAMXD,6, PA4T, PA5T, PA-6T,PA5T, PA10T, PA12T, PA4I, PA5I, PA-61, PA10I, copolymers, terpolymers,or any mixtures thereof. Copolymers, terpolymers, and mixtures thereofare contemplated as feedstock components, as long as the resultantfeedstock, e.g., the base polyamide composition, comprises somecaprolactam units.

In some aspects, the polyamide feedstock may comprise polyamidesproduced through ring-opening polymerization or polycondensation,including the copolymerization and/or copolycondensation, of lactams.For example, these polyamides may include, for example, those producedfrom propriolactam, butyrolactam, valerolactam, caprolactam,laurolactam, undecylolactam, and enantholactam. In some embodiments, thepolyamide is a polymer derived from the polymerization of caprolactam,and as such, the nylon mixture includes some polymers having caprolactamunits (non-residual caprolactam).

In one embodiment, the polyamide composition may comprise the polyamidesproduced through the copolymerization of a lactam with a nylon, forexample, the product of the copolymerization of a caprolactam withPA-6,6.

In some embodiments, the nylon mixture may be the condensation productsof one or more dicarboxylic acids, one or more diamines, one or moreaminocarboxylic acids, and/or ring-opening polymerization products ofone or more cyclic lactams, e.g., caprolactam and laurolactam. In someaspects, the polyamide feedstock may include aliphatic, aromatic, and/orsemi-aromatic polyamides and can be homopolymer, copolymer, terpolymeror higher order polymers. In some aspects, the polyamide feedstockincludes blends of two or more polyamides. In some embodiments, thepolyamide feedstock comprises aliphatic or aromatic polyamides or blendsof two or more polyamides.

In some aspects, the dicarboxylic acids may comprise one or more ofadipic acid, azelaic acid, terephthalic acid, isophthalic acid, sebacicacid, and dodecanedioic acid. In some aspects, the dicarboxylic acidsmay comprise adipic, isophthalic and terephthalic acid. In some aspects,the dicarboxylic acids may comprise an aminocarboxylic acid, e.g.,11-aminododecanoic acid.

In some aspects, the diamines may comprise one or more oftetramethylenediamine, hexamethylenediamine, octamethylenediamine,nonamethylenediamine, 2-methylpentamethylenediamine,2-methyloctamethylenediamine, trimethylhexamethylenediamine,bis(p-aminocyclohexyl)methane, m-xylylenediamine, p-xylylenediamine,decamethylenediamine, undecamethylenediamine, dodecamethylenediamine,tridecamethylenediamine, tetramethylenediamine, pentamethylenediamine,hexamethylenediamine, and the like. Other examples of the aromaticdiamine components, which are merely illustrative, include benzenediamines such as 1,4-diaminobenzene, 1,3-diaminobenzene, and1,2-diaminobenzene; diphenyl(thio)ether diamines such as4,4′-diaminodiphenylether, 3,4′-diaminodiphenylether,3,3′-diaminodiphenylether, and 4,4′-diaminodiphenylthioether;benzophenone diamines such as 3,3′-diaminobenzophenone and4,4′-diaminobenzophenone; diphenylphosphine diamines such as3,3′-diaminodiphenylphosphine and 4,4′-diaminodiphenylphosphine;diphenylalkylene diamines such as 3,3′-diaminodiphenylmethane,4,4′-diaminodiphenylmethane, 3,3′-diaminodiphenylpropane, and4,4′-diaminodiphenylpropane; diphenylsulfide diamines such as3,3′-diaminodiphenylsulfide and 4,4′-diaminodiphenylsulfide;diphenylsulfone diamines such as 3,3′-diaminodiphenylsulfone and4,4′-diaminodiphenylsulfone; and benzidines such as benzidine and3,3′-dimethylbenzidine.

In some aspects, the polyamide feedstock comprises physical blends ofaliphatic polyamides, semiaromatic polyamides, and/or aromaticpolyamides to obtain properties intermediate between or synergistic ofthe properties of each polyamide.

While much of the discussion above relates to polyamide feedstock, andin particular copolyamides of PA-6,6 and PA-6, it is contemplated thatthe processes and compositions described herein my include or relate topolyamides ranging from aliphatic polyamides (traditionally PA-6,6 andPA-6 or other aliphatic nylons) to copolyamides with aromatic components(for example paraphenylenediamine and terephthalic acid), to copolymerssuch as adipate with 2-methyl pentmethylene diamine and3,5-diacarboxybenzenesulfonic acid (or sulfoisophthalic acid in the formof its sodium sulfonate salt).

Other polyamides are described in U.S. Provisional Patent ApplicationNo. 62/690,748, which is incorporated by reference herein.

In one embodiment, the nylon mixture comprises nylon-6 and nylon-6,6.The nylon-6 may be present in the nylon mixture in an amount rangingfrom 1 wt % to 80 wt %, e.g., from 1 wt % to 60 wt %, from 1 wt % to 50wt %, from 10 wt % to 60 wt %, from 5 wt % to 50 wt %, from 5 wt % to 40wt %, from 7 wt % to 40 wt %, from 5 wt % to 35 wt %, from 10 wt % to 35wt %, from 10 wt % to 30 wt %, or from 15 wt % to 30 wt %. In terms ofupper limits, the nylon-6 may be present in the nylon mixture in anamount less than 80 wt %, e.g., less than 70 wt %, less than 60 wt %,less than 55 wt %, less than 50 wt %, less than 45 wt %, less than 40 wt%, less than 35 wt %, or less than 30 wt %. In terms of lower limits,the nylon-6 may be present in the nylon mixture in an amount greaterthan 1 wt %, e.g., greater than 2 wt %, greater than 3 wt %, greaterthan 4 wt %, greater than 5 wt %, greater than 7 wt %, greater than 10wt %, greater than 12 wt %, greater than 15 wt %, greater than 20 wt %,greater than 25 wt %, or greater than 30 wt %.

The nylon-6,6 may be present in the nylon mixture in an amount rangingfrom 20 wt % to 99 wt %, e.g., from 40 wt % to 95 wt %, from 50 wt % to95 wt %, from 55 wt % to 85 wt %, from 65 wt % to 95 wt %, from 60 wt %to 90 wt %, from 65 wt % to 90 wt %, from 70 wt % to 90 wt %, from 75 wt% to 85 wt %, or from 70 wt % to 85 wt %. In terms of upper limits, thenylon-6,6 may be present in the nylon mixture in an amount less than 99wt %, e.g., less than 95 wt %, less than 90 wt %, less than 85 wt %,less than 80 wt %, less than 75 wt %, or less than 70 wt %. In terms oflower limits, the nylon-6,6 may be present in the nylon mixture in anamount greater than 20 wt %, e.g., greater than 40 wt %, greater than 50wt %, greater than 55 wt %, greater than 60 wt %, greater than 65 wt %,greater than 70 wt %, or greater than 75 wt %.

The base polyamide composition may be produced by polymerizingcaprolactam monomers (that may be within other mixtures such asnylon-6,6 salt), which provides for at least some caprolactam unitcontent in the nylon mixture. Such caprolactam units are not consideredto be “residual” caprolactam. In some embodiments, the base polyamidecomposition comprises greater than 1.4 wt % caprolactam units, based onthe total weight of the base polyamide composition, e.g., greater than1.5 wt %, greater than 2 wt %, greater than 3 wt %, greater than 4 wt %,greater than 5 wt %, greater than 7 wt %, greater than 10 wt %, greaterthan 15 wt %, greater than 20 wt %, or greater than 25 wt %. In terms ofranges, the base polyamide composition may comprise caprolactam units inan amount ranging from 1.4 wt % to 50 wt %, e.g., from 1.5 wt % to 45 wt%, from 2 wt % to 43 wt %, from 3 wt % to 40 wt %, from 4 wt % to 35 wt%, from 5 wt % to 30 wt %, from 10 wt % to 30 wt %, or from 10 wt % to20 wt %. In terms of upper limits, the base polyamide composition maycomprise less than 50 wt % caprolactam units, e.g., less than 45 wt %,less than 43 wt %, less than 40 wt %, less than 35 wt %, less than 30 wt%, or less than 20 wt %.

In addition to the non-residual caprolactam units in the nylon mixture,the base polyamide composition also comprises undesirable, low molecularweight components, e.g., residual caprolactam. These low molecularweight compounds form as by-products, or unreacted monomers, of thepolymerization reaction, and have detrimental effects on the propertiesof the final polyamide composition that may result, e.g., after SSP,therefrom. For example, the low-molecular weight compounds maydetrimentally affect products, e.g., injection-molded products, bydiffusing on the surface thereof, thus forming a greasy film. Thesediffused low molecular weight compounds may also impair the surfaceappearance of the products, e.g., reduced gloss and impaired colorimpression. Still further, the residual caprolactam can detrimentallyresult in: (1) build up/plate out on process equipment surfaces leadingto downtime or reduced production throughput; (2) a non-food contactcompliant product according to regulatory specifications, e.g., FDA foodcontact compliance; and (3) interference with adhesion between filmlayers, e.g., ethylene vinyl alcohol layers or polyethylene-s-maleicanhydride layers.

In some embodiments, the base polyamide composition comprises greaterthan 0.6 wt % residual caprolactam, based on the total weight of thebase polyamide composition, e.g., greater than 0.7 wt %, greater than0.75 wt %, greater than 0.8 wt %, greater than 1 wt %, greater than 1.2wt %, greater than 1.5 wt %, greater than 1.7 wt %, greater than 2 wt %,greater than 2.2 wt %, greater than 2.5 wt %, greater than 2.7 wt %,greater than 3 wt %, or greater than 3.5 wt %. In terms of ranges, thebase polyamide composition may comprise residual caprolactam in anamount ranging from 0.6 wt % to 10 wt %, e.g., from 0.7 wt % to 10 wt %,from 0.8 wt % to 9 wt %, from 0.9 wt % to 8.5 wt %, from 1 wt % to 8 wt%, from 1 wt % to 7 wt %, from 1.5 wt % to 5 wt %, from 1.5 wt % to 4 wt%, from 1.5 wt % to 2.5 wt %, or from 1.7 wt % to 2 wt %. In terms ofupper limits, the base polyamide composition may comprise less than 10wt % residual caprolactam, e.g., less than 9 wt %, less than 8.5 wt %,less than 8 wt %, less than 7 wt %, less than 5 wt %, less than 3 wt %,less than 2.5 wt % or less than 2 wt %.

It is noted that the residual caprolactam concentration in the finalpolyamide composition may be less than the residual caprolactamconcentration in the base polyamide composition. Residual caprolactamconcentration in the final polyamide composition is discussed in detailbelow.

In some embodiments, the base polyamide composition has an RV(initially, before processing) less than 55, e.g., less than 53, lessthan 50, less than 48, less than 45, less than 43, less than 40, lessthan 38, less than 35, less than 33, less than 30, less than 25, lessthan 20, or less than 15. In terms of lower limits, the base polyamidecomposition may have an RV greater than 1, e.g., greater than 3, greaterthan 5, greater than 8, greater than 10, greater than 12, greater than15, or greater than 20. In terms of ranges, the base polyamidecomposition may have an RV ranging from 1 to 55, e.g., from 1 to 50,from 1 to 45, from 3 to 40, from 5 to 38, from 10 to 38, from 10 to 35,from 25 to 40, from 20 to 40, from 30 to 40, from 15 to 40, from 15 to30, or from 20 to 35. RV, as discussed herein, may be measured by theformic acid method, e.g., ASTM D789 (9.34) (2018), which is well knownin the art.

In some embodiments, the base polyamide composition has a number averagemolecular weight, M_(n), (initially, before processing) less than 18,000g/mol, e.g., less than 15,000 g/mol, less than 13,000 g/mol, less than12,000 g/mol, less than 11,000 g/mol, less than 1,000 g/mol, or lessthan 8,000 g/mol. In terms of ranges, the base polyamide composition mayhave a number average molecular weight, M_(n), ranging from 2,000 g/molto 18,000 g/mol, e.g., from 4,000 g/mol to 15,000 g/mol, from 5,000g/mol to 12,000 g/mol, or from 7,000 g/mol to 11,000 g/mol. In terms oflower limits, the base polyamide composition may have a number averagemolecular weight greater than 2,000 g/mol, e.g., greater than 4,000g/mol, greater than 5,000 g/mol, greater than 7,000 g/mol, or greaterthan 9,000 g/mol.

In some embodiments, the base polyamide composition has a melting pointranging from 185° C. to 255° C., e.g., from 205° C. to 255° C., from185° C. to 240° C., from 190° C. to 230° C., from 195° C. to 215° C.,from 200° C. to 210° C., or from 202° C. to 208° C. In terms of upperlimits, the base polyamide composition may have a melting point lessthan 255° C., e.g., less than 240° C., less than 230° C., less than 215°C., less than 210° C., or less than 208° C. In terms of lower limits,the base polyamide composition may have a melting point greater than185° C., e.g., greater than 190° C., greater than 195° C., greater than200° C., greater than 202° C., or greater than 205° C.

It has been found that the use of base polyamide compositions havingthese melting point have a synergistic result when employed in the SSPprocesses discussed herein. One theory for this is that base polyamidecompositions having lower melting points may not be able to reachsufficient temperatures to achieve caprolactam removal. By employinghigher melting point base compositions, the ability for caprolactamremoval is effectively facilitated. Also, if the melting point of thebase polyamide compositions is too low, the composition will melt duringSSP, thus rendering the product ineffective.

In some cases, the base polyamide composition is produced by meltpolymerizing a polyamide composition and pelletizing the meltedpolyamide composition to form polyamide pellets.

Process for Producing a Final Polyamide Composition

In conventional processes, undesirable, low molecular weight components,e.g., residual caprolactam, are often removed, e.g., by extraction.Extraction is normally carried out with hot water or with liquids thatcontain mostly water. From these extraction waters, the residualcaprolactam can be recaptured, cleaned, and in some cases, reintroducedas a recycle stream to the polymerization process. These separate steps,however, detrimentally add equipment and operating costs and can addcolor to the resin. As noted above, an alternative process to waterextraction is to remove the residual caprolactam as part of the SSPprocess, where the caprolactam is volatilized at SSP temperatures andremoved from the reactor.

Disclosed herein is a process for producing a polyamides having a lowresidual caprolactam concentration is disclosed herein. The processcomprises the steps of providing the base polyamide composition andprocessing the base polyamide composition to form the final polyamidecomposition. The base polyamide composition has an initial residualcaprolactam concentration and an initial RV (see discussion above).Likewise, the final polyamide composition has a final residualcaprolactam concentration and a final RV.

The processing may be conducted at specific operating parameters thatprovide for synergistic results when employed with the base polyamidecompositions disclosed herein.

In some embodiments, the processing is conducted for a build time lessthan 40 hours, e.g. less than 38 hours, less than 36 hours, less than 35hours, less than 34 hours, less than 32 hours, less than 30 hours, lessthan 28 hours, less than 26 hours, less than 25 hours, less than 24hours, less than 22 hours, or less than 20 hours. In terms of ranges,the processing may be conducted for a build time ranging from 1 hour to40 hours, e.g., from 2 hours to 38 hours, from 4 hours to 36 hours, from5 hours to 35 hours, from 6 hours to 34 hours, from 8 hour to 32 hours,from 10 hours to 30 hours, from 12 hour to 28 hours, from 14 hours to 26hours, from 16 hour to 25 hours, or from 18 hours to 24 hours. In termsof lower limits, the processing may be conducted for a build timegreater than 1 hour, e.g., greater than 2 hours, greater than 4 hours,greater than 6 hours, greater than 8 hours, greater than 10 hours,greater than 12 hours, greater than 14 hours, or greater than 15 hours.

In some embodiments, formulation/process provides for an advantageous RVbuild rate, which provides sufficient time for beneficial caprolactamremoval and final polyamide composition RV. In some embodiments, the RVbuild rate ranges from 1 to 30 RV units/hour, e.g., from 1 to 27 RVunits/hour, from 1 to 25 RV units/hour, from 1 to 22 RV units/hour, from1.5 to 19 RV units/hour, from 1.5 to 17 RV units/hour, from 1.5 to 15 RVunits/hour, from 1 to 12 RV units/hour, from 1.5 to 12 RV units/hour,from 1 to 9 RV units/hour, or from 1.5 to 9 RV units/hour. In terms ofupper limits, the RV build rate may be less than 30 RV units/hour, e.g.,less than 28 RV units/hour, less than 26 RV units/hour, less than 25 RVunits/hour, less than 23 RV units/hour, less than 20 RV units/hour, lessthan 19 RV units/hour, less than 18 RV units/hour, less than 16 RVunits/hour, less than 15 RV units/hour, less than 14 RV units/hour, lessthan 13 RV units/hour, less than 12 RV units/hour, less than 11 RVunits/hour, less than 10 RV units/hour, less than 9 RV units/hour, lessthan 8 RV units/hour, less than 7 RV units/hour, less than 6 RVunits/hour, or less than 5 RV units/hour. In terms of lower limits, theRV build rate may be greater than 0.1 RV units/hour, e.g., greater than0.3 RV units/hour, greater than 0.3 RV units/hour, greater than 0.5 RVunits/hour, greater than 0.7 RV units/hour, greater than 1 RVunits/hour, greater than 1.2 RV units/hour, or greater than 1.5 RVunits/hour. Of course, these ranges and limits related to only someembodiments. In other embodiments, higher RV build rates arecontemplated, e.g., build rates greater than 30 RV units/hour.

In some embodiments, the processing may be conducted at a temperatureranging from 150° C.-250° C., e.g., from 160° C.-230° C., from 165°C.-210° C., from 170° C.-190° C., or from 175° C.-185° C. In terms ofupper limits, the processing may be conducted at a temperature less than250° C., e.g., less than 230° C., less than 210° C., less than 190° C.,or less than 185° C. In terms of lower limits, the processing may beconducted at a temperature greater than 150° C., e.g., greater than 160°C., greater than 165° C., greater than 175° C. or greater than 175° C.

In some embodiments, the processing is conducted at a pressure below 1atm, e.g., below 0.75 atm, below 0.5 atm, below 0.25 atm, or below 0.1atm. In one embodiment, the processing is conducted at a pressure lessthan atmospheric pressure.

In a particular embodiment, the temperature, pressure, and build timeare synergistically used together. For example, the processing may beconducted at temperature ranging from 150° C.-250° C., a build time lessthan 30 hours, and a pressure less than atmospheric pressure. In somecases, the entire process time (the “recipe time”) may range from 15hours to 35 hours, e.g., from 5 hours to 30 hours, from 18 hours to 24hours, or from 20 hours to 22 hours. Each of these factors may impactthe RV and the residual caprolactam concentration of the final polyamidecomposition, and can be adjusted and/or balanced to achieve desiredresults.

The components of the base polyamide composition provide for theseparticular build times, which allow for both sufficient caprolactamremoval and sufficient RV and/or molecular weight build. Conventionalbase polyamide compositions have been unable to achieve thiscombination.

The processing step may vary widely. In some cases, the processing stepcomprises SSP, and in such cases the SSP may comprise heating the basepolyamide. In these instances, the SSP may be conducted at a temperatureranging from 170° C.-190° C., e.g., from 175° C.-190° C., from 175°C.-188° C., from 180° C.-190° C., or from 182° C.-188° C. In terms ofupper limits, the processing may be conducted at a temperature less than190° C., e.g., less than 188° C., less than 185° C., or less than 182°C. In terms of lower limits, the processing may be conducted at atemperature greater than 170° C., e.g., greater than 175° C., greaterthan 180° C., or greater than 182° C.

In other embodiments, the processing step comprises and extrusion RVbuild, e.g., using twin screw extrusion. The processing is not limitedto these exemplary options, however. Other examples include extractionand/or leaching. These steps may be carried out under low pressure orunder vacuum.

Advantageously, the removal of residual caprolactam via SSP has beenfound to retard the propensity for plate-out of the residual caprolactammonomer on metal surfaces. Plate-out typically occurs when the residualcaprolactam monomer volatilizes from the polymer melt at high processingtemperatures and then condenses on metal surfaces of the processingequipment. This plate-out, generates harmful flaws and defects in thefilms and/or other end products. The reduction or elimination ofresidual caprolactam in the polyamide beneficially leads to reduction orelimination of plate-out. The processes also beneficially producepolyamides that comply with FDA regulation (21 CFR 177.1500 (b) (4.1)),which requires low amounts of residual caprolactam for food contactapplications. Additionally, SSP prevents residual caprolactam fromblooming to the film surface which can cause various problems such asreduced adhesion with other polymer film layers, e.g., maleatedpolyethylene, poly(ethylene vinyl alcohol), and creates haze whichlimits film clarity.

In some embodiments, the processing step increases the initial RV of thebase polyamide composition and/or decreases the initial residualcaprolactam concentration of the base polyamide composition. In somecases, the final RV is at least 10% greater than the initial RV, e.g.,at least 15% greater, at least 20% greater, at least 25% greater, atleast 30% greater at least 35% greater, at least 40% greater, at least50% greater, at least 60% greater, at least 75% greater, at least 90%greater, or at least 100% greater.

In some embodiments, the final caprolactam concentration is at least 5%less than the initial caprolactam concentration, e.g., at least 10%less, at least 15% less, at least 20% less, at least 25% less at least35% less, at least 45% less, at least 50% less, at least 60% less, atleast 75% less, at least 90% less, or at least 100% less.

In some embodiments, the final polyamide composition comprises less than0.75 wt % residual caprolactam, based on the total weight of the finalpolyamide composition, e.g., less than 0.70 wt %, less than 0.65 wt %,less than 0.6 wt %, less than 0.55 wt %, less than 0.5 wt %, less than0.45 wt %, less than 0.4 wt %, less than 0.35 wt %, less than 0.3 wt %,less than 0.25 wt %, or less than 0.2 wt %. In terms of ranges, thefinal polyamide composition may comprise residual caprolactam in anamount ranging from 0.01 wt % to 0.7 wt %, e.g., from 0.05 wt % to 0.7wt %, from 0.1 wt % to 0.6 wt %, from 0.2 wt % to 0.6 wt %, from 0.2 wt% to 0.5 wt %, from 0.2 wt % to 0.4 wt %, or from 0.25 wt % to 0.35 wt%. In terms of upper limits, the final polyamide composition maycomprise greater than 0.01 wt % residual caprolactam, e.g., greater than0.05 wt %, greater than 0.1 wt %, greater than 0.15 wt %, greater than0.2 wt %, greater than 0.25 wt %, greater than 0.3 wt %, or greater than0.4 wt %. In some aspects, the high molecular weight polyamide solutioncomprises substantially no (residual) caprolactam, e.g., no (residual)caprolactam.

In some embodiments, the final polyamide composition has an RV (afterprocessing) ranging from 40 to 350, e.g., from 45 to 300, from 50 to250, from 55 to 215, from 55 to 200, from 50 to 200, from 55 to 190,from 70 to 175, from 120 to 180, from 130 to 170, from 140 to 160, from75 to 160, from 80 to 100, from 85 to 140, from 90 to 135, from 85 to95, or from 100 to 130. In terms of lower limits, the final polyamidecomposition may have an RV greater than 40, e.g., greater than 45,greater than 50, greater than 55, greater than 60, greater than 65,greater than 70, greater than 75, greater than 80, greater than 90,greater than 95, greater than 100, greater than 110, greater than 120,or greater than 130. In terms of upper limits, the final polyamidecomposition may have an RV less than 350, e.g., less than 300, less than250, less than 300, less than 250, less than 200, less than 190, lessthan 175, less than 170, less than 160, less than 140, less than 135,less than 130, less than 120, less than 110, less than 100, less than90.

As noted herein, the combination of the disclosed base polyamidecomposition and processing step provides for surprising benefitsrelating to pellet quality. In one embodiment, the final polyamidecomposition has a color index ranging from −6.0 to 5.0, as measured byASTM E313 (2018), e.g., from −5.5 to 4.5, from −5.0 to 4.0, from −4.5 to3.5, from −4.0 to 3.0, from −3.5 to 2.5, from −3.0 to 2.0, from −2.5 to1.5, from −2.0 to 1.0, from −1.5 to 0.5, or from −1.0 to 0. In terms ofupper limits, the final polyamide composition may have a color indexless than 5.0, e.g., less than 5.5, less than 5.0, less than 5.5, lessthan 5.0, less than 4.5, less than 4.0, less than 3.5, less than 3.0,less than 2.5, less than 2.0, less than 1.5, less than 1.0, less than0.5, or less than 0. In terms of lower limits, the final polyamidecomposition may have a color index greater than −6.0, e.g., greater than−5.5, greater than −5.5, greater than −5.0, greater than −4.5, greaterthan −4.0, greater than −3.5, greater than −3.0, greater than −2.5,greater than −2.0, greater than −1.5, greater than −1.0, greater than−0.5, or greater than 0.

In some cases, color index, e.g., yellowness index, is calculatedaccording to ASTM E313 employing a spectrophotometer (an example brandis BYK Gardner). The yellowness index is an indicator of the whitenessor yellowness of an analyzed material; the lower the number relates to awhiter or less yellow material. In some cases, yellowness index valuesmay be calculated using an adjustment factor, so in some cases, it maybe more useful to compare data on a b* basis, which depicts theyellowness or blueness of a sample. Lower or negative values correspondto blue or whitish pellets that have an absence of a yellow hue. Thebelow is a graph that show demonstrates the BYK Gardner unit'scorrelation between YI and b*.

In some cases, the disclosed formulation and/or the SSP processcontribute to the final polyamide composition having a consistent size,e.g., a high degree of pellet size uniformity, which may be expressed asweight per pellets (or per 100 pellets). Without being bound by theory,it is believed that the use of the disclosed parameters, e.g., RVranges/limits, contributes to the elimination of bubbles from the moltenpolyamide strands, which results in less disruption in strand anddiameter consistency. For example, the final polyamide composition mayhave a pellet weight ranging from 0.50 grams/100 pellets to 1.4grams/100 pellets, e.g., from 0.55 grams/100 pellets to 1.35 grams/100pellets, from 0.60 grams/100 pellets to 1.30 grams/100 pellets, from0.65 grams/100 pellets to 1.25 grams/100 pellets, from 0.70 grams/100pellets to 1.20 grams/100 pellets, from 0.75 grams/100 pellets to 1.15grams/100 pellets, or from 0.80 grams/100 pellets to 1.10 grams/100pellets. In terms of upper limits, the final polyamide composition mayhave a pellet weight less than 1.4 grams/100 pellets, e.g., less than1.35 grams/100 pellets, less than 1.30 grams/100 pellets, less than 1.25grams/100 pellets, less than 1.20 grams/100 pellets, less than 1.15grams/100 pellets, or less than 1.10 grams/100 pellets. In terms oflower limits, the final polyamide composition may have a pellet weightgreater than 0.50 grams/100 pellets, e.g., greater than 0.55 grams/100pellets, greater than 0.60 grams/100 pellets, greater than 0.65grams/100 pellets, greater than 0.70 grams/100 pellets, greater than0.75 grams/100 pellets, or greater than 0.80 grams/100 pellets. In somecases, the final polyamide composition may have a pellet weight thatvaries by only +/−25%, based on the average or target pellet weight,e.g., +/−20%, +/−15%, +/−10%, +/−5%, or +/−2%.

In some cases, the improved color quality advantageously allows for thereduction or elimination of tinting agent(s) in the final polyamidecomposition. For example, the final polyamide composition compriseslittle or no tinting agent(s). In one embodiment, the final polyamidecompositions comprise from 0 wt % to 10 wt % tinting agent, based on thetotal weight of the final polyamide composition, e.g., from 0.0001 wt %to 10 wt %, from 0.001 to 10 wt %, from 0.005 wt % to 0.5 wt %, from0.05 to 0.5 wt %, from 0.05 to 0.5 wt %, or from 0.005 to 0.1 wt %. Interms of upper limits, the final polyamide compositions comprise lessthan 10 wt % tinting agent, e.g., less than 9 wt %, less than 8 wt %less than 7 wt %, less than 6 wt %, less than 5 wt %, less than 4 wt %,less than 3 wt %, less than 2 wt %, less than 1 wt %, less than 0.5 wt%, less than 0.1 wt %, or less than 0.05 wt %. In terms of lower limits,the final polyamide compositions comprise greater than 0.0001 wt %tinting agent, e.g., greater than 0.005 wt %, greater than 0.001 wt %,greater than 0.05 wt %, greater than 0.01 wt %, or greater than 0.1 wt%. These ranges and limits are applicable to the base polyamidecomposition as well.

In one specific embodiment, the disclosed base polyamide composition andprocess provide are utilized. The base polyamide composition comprisesfrom 0.1 wppm to 30 wppm catalyst composition, from 1 wt % to 8 wt %residual caprolactam and has a delta end group level ranging from 50μeq/gram to 75 μeq/gram and has an initial RV less than 35. The finalpolyamide composition comprises less than 0.5 wt % residual caprolactamand has a final RV greater than 45.

In another specific embodiment, the disclosed base polyamide compositionand process provide are utilized. The base polyamide compositioncomprises from 1 wppm to 15 wppm phosphorus, greater than 1.5 wt %residual caprolactam and has a delta end group level greater than 50μeq/gram and has an initial RV less than 33. The processing is conductedat a pressure less than atmospheric pressure and a temperature rangingfrom 175° C. to 185° C. The final polyamide composition comprises lessthan 0.4 wt % residual caprolactam and has a final RV greater than 75.

Films and Other Applications

As noted above, one specific application for the disclosed polyamidecompositions is in films, e.g., films for food-related applications.Also disclosed herein is a film formed from the final polyamidecomposition. Film production processes are well known, and the processfor forming the film from the final polyamide composition may varywidely.

In other cases, the disclosed polyamide compositions may be particularlyuseful for molding-related applications. Other exemplary applicationsinclude extruded profiles, fiber, blow molding, and/or otherapplications that require low caprolactam concentration.

The films have surprising performance characteristics. For example, thefilms may demonstrate a puncture resistance greater 3 J/mm, as measuredvia ASTM F1366 (2018), e.g., greater than 4 J/mm, greater than 5 J/mm,greater than 7 J/mm, greater than 10 J/mm, or greater than 15 J/mm. Interms of ranges, the films may demonstrate a puncture resistance rangingfrom 3 J/mm to 50 J/mm, e.g., from 3 J/mm to 25 J/mm, from 5 J/mm to 50J/mm, from 5 J/mm to 25 J/mm, from 5 J/mm to 20 J/mm, or 10 J/mm to 25J/mm.

In some embodiments, the films may demonstrate an impact resistancegreater than 1500 grams, as measured via ASTM D1709 A (2018), e.g.,greater than 1700 grams, greater than 2000 grams, greater than 2200grams, greater than 2500 grams, greater than 3000 grams or greater than5000 grams. In terms of ranges, the films may demonstrate an impactresistance ranging from 1500 grams to 20000 grams, e.g., from 1700 gramsto 15000 grams, from 2000 grams to 15000 grams, from 2000 grams to 10000grams, from 2500 grams to 10000 grams, or from 3000 grams to 10000grams.

In some embodiments, the films may demonstrate a tear resistance greaterthan 50 grams, as measured via ASTM D1922 (2018), e.g., greater than 60grams, greater than 70 grams, greater than 80 grams, greater than 90grams, greater than 100 grams, greater than 125 grams, or greater than150 grams. In terms of ranges, the films may demonstrate tear resistanceranging from 50 grams to 500 grams, e.g., from 60 grams to 450 grams,from 70 grams to 400 grams, from 80 grams to 300 grams, from 80 grams to200 grams, or from 90 grams to 150 grams.

Unexpectedly, the inventors have discovered that higher (positive)levels of DEG in the final polyamide composition contributes filmshaving better adhesion between layers, when utilized in multi-layer filmapplications. In particular, it has been found that that these filmshave improved bonding strength with tie layers, e.g., maleicanhydride-based tie layers, of multi-layer film applications. Thisimprovement in bonding has been shown to contribute to improvedproperties, e.g., puncture resistance, impact resistance, and/or tearresistance, in the multi-layer film structures, as noted above. Withoutbeing bound by theory, it is postulated that the increased level amineends (as reflected in higher DEG level) surprisingly improves adhesionbetween other layers, e.g., polyethylene, polyethylene terephthalate,and/or other polyamide layers. The amine ends allow more/better bonds toform with maleic anhydride-based tie layers, which results insignificant improvements in lamination, e.g., reduction or eliminationof delamination.

The final polyamide composition, in some embodiments, has a DEG levelgreater than 20 μeq/gram, e.g., greater than 22 μeq/gram, greater than25 μeq/gram, greater than 27 μeq/gram, greater than 30 μeq/gram, greaterthan 32 μeq/gram, greater than 35 μeq/gram, greater than 40 μeq/gram,greater than 45 μeq/gram, greater than 50 μeq/gram, or greater than 55μeq/gram.

In terms of ranges, the final polyamide composition may have a DEGranging from 5 μeq/gram to 125 μeq/gram, e.g., from 10 μeq/gram to 120μeq/gram, from 15 μeq/gram to 115 μeq/gram, from 20 μeq/gram to 110μeq/gram, from 25 μeq/gram to 100 μeq/gram, from 30 μeq/gram to 90μeq/gram, from 35 μeq/gram to 85 μeq/gram, or from 40 μeq/gram to 80μeq/gram. In terms of upper limits, the base polyamide composition mayhave a DEG level less than 125 μeq/gram, e.g. less than 120 μeq/gram,less than 115 μeq/gram, less than 110 μeq/gram, less than 100 μeq/gram,less than 90 μeq/gram, less than 80 μeq/gram, less than 70 μeq/gram,less than 68 μeq/gram, less than 65 μeq/gram, less than 63 μeq/gram,less than 60 μeq/gram, less than 58 μeq/gram, less than 55 μeq/gram,less than 53 μeq/gram, or less than 50 μeq/gram.

Tunable Aspects

The present disclosure is directed, in part, to a tunable method formaking final polyamide compositions, and for controlling finalcaprolactam concentrations and/or final RVs of the final polyamidecompositions. The final polyamide compositions may be “tuned” byadjusting a variety of conditions during the processing step and/or byadjusting the make-up of the base polyamide composition so as to achieveone or more desirable properties. In some aspects, the residualcaprolactam concentration and/or RV of the final polyamide composition(as well as other characteristics thereof) may be controlled to bewithin the ranges and limits discussed above.

Process conditions and/or compositional features that may be adjustedduring the processing include, for example, DEG level (end groupbalance), catalyst content, temperature, pressure moisture content, andthe presence of the catalyst. By adjusting at least one of theseconditions, the desired properties of the final polyamide compositioncan be controlled, e.g., tuned. The inventors have discovered that thecharacteristics of the precursor polyamide can be adjusted by utilizingparticular parameters such that a desirable end product can be achieved.These specific relationships between base polyamide composition,operating conditions, and final polyamide composition have not yet beensufficiently explored and/or disclosed in the existing references.

In one embodiment, disclosed herein is a process for controlling therelative viscosity of a final polyamide composition. The processcomprises the step of providing a base polyamide composition having alow relative viscosity, e.g., less than 40. The process furthercomprises that steps of determining a desired relative viscosity for thefinal polyamide composition and selecting at least one processingcondition from catalyst content, DEG level, temperature, pressure, andmoisture content. The process further comprises the “tunable” step ofprocessing the base polyamide composition under the at least oneprocessing condition and based on the desired relative viscosity to formthe final polyamide composition having a final relative viscosityranging from 55 to 200, e.g., from 75 to 200.

In one embodiment, disclosed herein is a process for controlling thecaprolactam content of a final polyamide composition. The processcomprises the step of providing a base polyamide composition havingresidual caprolactam content greater than 0.75 wt %. The process furthercomprises the steps of determining a desired residual caprolactamcontent for the final polyamide composition and selecting at least oneprocessing condition from catalyst content, DEG level, temperature,pressure, and moisture content. The process further comprises the“tunable” step of processing the base polyamide composition under the atleast one condition and based on the desired residual caprolactamcontent to form the final polyamide composition having a residualcaprolactam content less than 0.4 wt %.

In one embodiment, disclosed herein is a process for manufacturing afinal polyamide composition. The process comprises the step of providinga base polyamide composition having one or more initial propertiescomprising initial caprolactam content, initial relative viscosity, andinitial color index. The process further comprises the step ofdetermining one or more desired final properties for the final polyamidecomposition product, the properties comprising final caprolactamcontent, final relative viscosity, and color index. The process furthercomprises the “tunable” step of processing the base polyamidecomposition under one or more process conditions comprising catalystcontent, delta end group level, temperature, pressure, and moisturecontent and based on the desired final property to provide the finalpolyamide composition.

EXAMPLES

Base polyamide compositions were prepared by polymerizing a saltsolution of HMD and adipic acid, and a desired amount of caprolactam totune polymer melting point as well as other properties, e.g., as shownbelow in Table 1. The copolyamide comprised repeating 1:1 adipicacid-hexamethylene diamine units (PA-6,6) combined with repeating unitsfrom lactams such as caprolactam (PA-6). A phosphorous-containingcatalyst was added prior to the initial polymerization step. Closeattention was paid to the level of the catalyst in order to control RVbuild rate and desired targets of RV and residual caprolactam.

Similarly, DEG level was controlled by controlling the amount of excesshexamethylene diamine added to the polymerization solution. In the caseof no HMD excess, the copolyamides typically come out with a DEG (asdefined above) around −30, and this is a result of the high volatilityof HMD versus adipic acid. In order to produce high DEG copolyamideswith excess amines, HMD can be spiked in some excess to thepolymerization solution. As one example, to target a DEG=45 μeq/gram,the HMD spike level can be approximately 38 μeq/gram.

The copolyamide was then polymerized by (a) heating the blend withstirring; (b) holding the blend under a suitable pressure andtemperature with removal of water vapor; followed by (c) decompressionand holding at a temperature above the melting point of the blend.

At the end of the polymerization process, the polymer was cooled withwater and extruded in the form of rods. These rods were subsequently cutin order to produce pellets.

The resultant base polyamide composition pellets were processed via SSPto build RV and to reduce residual caprolactam concentration, yieldingfinal polyamide compositions. The SSP was conducted under an inertatmosphere, elevated temperatures, and under reduced pressure. Reducedpressures were achieved through the use of vacuum pumps. Thecompositions of the base and final polyamide compositions were measured.The results at various build times are presented in Table 1.

TABLE 1 Working and Comparative Example Compositions Catalyst(Phosphorus), Build SSP Final DEG ppm Time, hr Temp. ° C. Final RVCapro, wt % Ex. 1 45 11 8 176.5 56 0.54 2 45 11 10 177 74.6 0.39 3 45 1112 177 102 0.29 4 45 11 14 177.5 132 0.24 5 45 11 16 178 155.3 0.21 6 4511 18 177 181 0.17 7 45 11 20 177.5 202 0.16 8 45 11 21 178 210 0.14 952 7 14 180 62.2 0.54 10 52 7 16.5 180 85.8 0.43 11 52 7 18.5 180 1050.3 12 52 7 20.5 180 125 0.25 13 52 7 22.5 180 138 0.21 14 52 7 24.5 180160 0.16 15 67 30 3 180 84.7 0.74 16 67 30 4 180 93.3 0.73 17 67 30 6180 107.2 0.58 18 67 30 24 180 159.6 0.14 Comparative Ex. A −30 150 4105 50.58 1.74 B −30 150 5 120 51.39 1.72 C −30 150 6 134 52.41 1.67 D−30 150 7 140 54.55 1.57 E −30 150 8 145 58.21 1.56 F −30 150 9 15165.43 1.54 G −30 150 10 152 75.24 1.48 H −30 150 11 157 90.15 1.43 I −30150 13 160 138.8 1.33

As shown in Table 1 and FIGS. 1-3, when base compositions comprisedspecific DEGs and catalyst concentrations within particular ranges andcatalyst concentration, significantly less residual caprolactam waspresent after processing (SSP), even at lesser build times. By employingspecific DEG levels and catalyst (phosphorus) concentrations, desirableRV build rates are achieved, which result in superior combinations ofresidual caprolactam concentration, e.g., less than 0.75, and RV, e.g.,greater than 40.

For example, Examples 1-8 utilized a DEG level of 45 and a catalystconcentration of 11 ppm. From a build time as low as 8 hours, thecompositions demonstrated low residual caprolactam levels and desirableRVs. From 8 hours to 21 hours, residual caprolactam ranged from 0.14 to0.54 and RV ranged from 56 to 210. Examples 9-14 utilized a DEG level of52 and a catalyst concentration of 7 ppm. From build times of at least14 hours, residual caprolactam ranged from 0.16 to 0.54 and RV rangedfrom 62 to 160. Examples 15-18 utilized a DEG level of 67 and a catalystconcentration of 30 ppm. From build times of at least 6 hours, residualcaprolactam ranged from 0.14 to 0.58 and RV ranged from 107.2 to 159.6.

FIG. 2 is a contour plot showing DEG levels and catalyst (phosphorus)concentration in base polyamide compositions. As shown, by employingspecific DEG levels and catalyst (phosphorus) concentrations, desirableRV build rates are achieved, which result in superior combinations ofresidual caprolactam concentration and RV. In particularly advantageousexamples, e.g., the top 6 contour bands, RV build rates less than 20 RVunits/hour were demonstrated, which resulted in low levels ofcaprolactam, e.g., significantly less than 0.6 wt %. In addition, theseexamples resulted in beneficial final RVs ranging from 55 to 215.

In contrast, when lower DEG levels, e.g., less than 30 μeq/gram, areutilized, rapid RV build rates were demonstrated. These rapid buildrates do not allow sufficient time for caprolactam removal. Thus, thefinal polyamide composition contained high levels of caprolactam, e.g.,significantly greater than 1 wt %.

FIG. 3 is a plot showing RV and residual caprolactam of Examples 9-14during solid state polymerization. As shown, employing specific DEGlevels and catalyst (phosphorus) concentrations resulted in superiorcombinations of residual caprolactam concentration and RV, even atlonger polymerization times, e.g., 24.5 hours. In particular, afterpolymerization for 16.5 hours, the final RV was 85.8 and the residualcaprolactam was 0.54 wt %. Surprisingly, after 8 more hours ofpolymerization, the RV build rate was controlled such that the final RVwas 160 and the final caprolactam was significantly less than 0.6 wt %.

The following embodiments are disclosed:

Embodiment 1

A process for producing a polyamide composition having a low residualcaprolactam concentration, the process comprising the steps of: (a)providing a base polyamide composition comprising: a nylon mixturehaving caprolactam units; from 1 wppb to 50 wppm of a catalystcomposition; and residual caprolactam, and having an initial residualcaprolactam concentration and an initial relative viscosity; (b)processing the base polyamide composition to form the final polyamidecomposition having a final residual caprolactam concentration and afinal relative viscosity.

Embodiment 2

An embodiment of embodiment 1, wherein the base polyamide compositionhas a delta end group level ranging from 30 μeq/gram to 90 μeq/gram.

Embodiment 3

An embodiment of embodiment 1 or 2, wherein the initial residualcaprolactam concentration is greater than 0.75 wt %, based on the totalweight of the base polyamide composition.

Embodiment 4

An embodiment of any of embodiments 1-3, wherein the final residualcaprolactam concentration is less than 0.75 wt %, based on the totalweight of the final polyamide composition.

Embodiment 5

An embodiment of any of embodiments 1-4, wherein the final relativeviscosity ranges from 40 to 350.

Embodiment 6

An embodiment of any of embodiments 1-5, wherein the final polyamidecomposition has a color index ranging from −6 to 5, as measured by ASTME313 (2018).

Embodiment 7

An embodiment of any of embodiments 1-6, wherein the final relativeviscosity is greater than the initial relative viscosity.

Embodiment 8

An embodiment of any of embodiments 1-7, wherein the final relativeviscosity is at least 10% greater than the initial relative viscosityand the final residual caprolactam concentration is at least 5% lessthan the initial residual caprolactam concentration.

Embodiment 9

An embodiment of any of embodiments 1-8, wherein, during processing, theinitial relative viscosity increases at a build rate that issubstantially linear, wherein the RV build rate ranges from 1 to 30 RVunits/hour.

Embodiment 10

An embodiment of any of embodiments 1-9, wherein the base polyamidecomposition has a melting point ranging from 180° C. to 255° C.

Embodiment 11

An embodiment of any of embodiments 1-10, wherein the nylon mixture ofthe base polyamide composition comprises: from 1 wt % to 80 wt %nylon-6; and from 20 wt % to 99 wt % nylon-6/6.

Embodiment 12

An embodiment of any of embodiments 1-11, wherein processing comprisessolid state polymerization, which comprises heating the base polyamide.

Embodiment 13

An embodiment of any of embodiments 1-12, wherein the processing isconducted for a build time ranging from 1 hour to 30 hours, and atemperature ranging from 170° C.-190° C.

Embodiment 14

An embodiment of any of embodiments 1-13, wherein the base polyamidecomposition is produced by melt polymerizing a polyamide composition andpelletizing the melted polyamide composition to form polyamide pellets.

Embodiment 15

An embodiment of any of embodiments 1-14, wherein the catalystcomposition comprises phosphorous acid; phosphonic acid; alkyl- andaryl-substituted phosphonic acids; 2-pyridylethyl phosphonic acid;hypophosphorous acid; alkyl-, aryl- and alkyl-/aryl-substitutedphosphinic acids; phosphoric acid; esters and salts of thesephosphorous-containing acids; manganese hypophosphite; sodiumhypophosphite; benzene phosphinic acid; monosodium phosphate; or anycombinations thereof.

Embodiment 16

An embodiment of any of embodiments 1-15, wherein processing isconducted at a temperature ranging from 150° C. to 250° C.

Embodiment 17

An embodiment of any of embodiments 1-16, wherein processing isconducted at a pressure less than atmospheric pressure.

Embodiment 18

An embodiment of any of embodiments 1-17, wherein the final polyamidecomposition comprises less than 10 wt % tinting agent and/or the basepolyamide composition comprises less than 10 wt % tinting agent.

Embodiment 19

An embodiment of any of embodiments 1-18, wherein the base polyamidecomposition comprises from 0.1 wppm to 30 wppm catalyst composition,from 1 wt % to 8 wt % residual caprolactam and has a delta end grouplevel ranging from 50 μeq/gram to 75 μeq/gram and has initial relativeviscosity less than 35 and wherein the final polyamide compositioncomprises less than 0.5 wt % residual caprolactam and has a finalrelative viscosity greater than 45.

Embodiment 20

An embodiment of any of embodiments 1-19, wherein the base polyamidecomposition comprises from 1 wppb to 35 wppm phosphorus, greater than1.5 wt % residual caprolactam and has a delta end group level greaterthan 50 μeq/gram and has initial relative viscosity less than 33 andwherein the processing is conducted at a pressure less than atmosphericpressure and a temperature ranging from 175° C. to 185° C., and whereinthe final polyamide composition comprises less than 0.4 wt % residualcaprolactam and has a final relative viscosity greater than 55, e.g.,greater than 75.

Embodiment 21

A base polyamide composition comprising: a nylon mixture havingcaprolactam units; from 1 wppb to 50 wppm catalyst composition; andgreater than 0.75 wt % residual caprolactam; wherein the base polyamidecomposition has a delta end group level ranging from 30 μeq/gram to 90μeq/gram.

Embodiment 22

An embodiment of embodiment 21, wherein the base polyamide compositionhas a delta end group level greater than 50 μeq/gram.

Embodiment 23

An embodiment of any of embodiments 21 and 22, wherein the basepolyamide comprises greater than 1.4 wt % caprolactam units, based onthe total weight of the base polyamide composition.

Embodiment 24

An embodiment of any of embodiments 21-23, wherein the base polyamidehas a relative viscosity less than 55.

Embodiment 25

An embodiment of any of embodiments 21-24, wherein the base polyamidehas a melting point ranging from 185° C. to 255° C.

Embodiment 26

An embodiment of any of embodiments 21-25, wherein the nylon mixture ofthe base polyamide composition comprises: from 1 wt % to 50 wt %nylon-6; and from 20 wt % to 99 wt % nylon-6/6.

Embodiment 27

An embodiment of any of embodiments 21-26, wherein the catalystcomposition comprises phosphorous acid; phosphonic acid; alkyl- andaryl-substituted phosphonic acids; 2-pyridylethyl phosphonic acid;hypophosphorous acid; alkyl-, aryl- and alkyl-/aryl-substitutedphosphinic acids; phosphoric acid; esters and salts of thesephosphorous-containing acids; manganese hypophosphite; sodiumhypophosphite; benzene phosphinic acid; monosodium phosphate; or anycombinations thereof.

Embodiment 28

A process for producing a polyamides having a low residual caprolactamconcentration, the process comprising the steps of: (a) providing a basepolyamide composition comprising: a nylon mixture having caprolactamunits; from 1 wppb to 50 wppm catalyst composition; and at least 0.75 wt% residual caprolactam; and having a delta end group level greater than50 μeq/gram, an initial caprolactam concentration, and an initialrelative viscosity; (b) processing the base polyamide composition toform a final polyamide composition having a final caprolactamconcentration and a final relative viscosity.

Embodiment 29

A film formed from a final polyamide composition comprising: polyamidemonomers; less than 0.75 wt % residual caprolactam, wherein the finalpolyamide composition has a delta end group level ranging from 30μeq/gram to 90 μeq/gram and a melting point ranging from 205° C. to 255°C.

Embodiment 30

An embodiment of embodiment 29, wherein the film demonstrates: apuncture resistance greater than 3 J/mm as measured via ASTM F1366(2018), an impact resistance greater than 1500 grams as measured viaASTM D1709. A (2018), and/or a tear resistance greater than 50 grams asmeasured via ASTM D1922 (2018).

Embodiment 31

A process for controlling the relative viscosity of a final polyamidecomposition, the process comprising: (a) providing a base polyamidecomposition having relative viscosity less than 40; (b) determining adesired relative viscosity for the final polyamide composition; (c)selecting at least one processing condition from catalyst content, deltaend group level, temperature, pressure, and moisture content; and (d)processing the base polyamide composition under the at least oneprocessing condition and based on the desired relative viscosity to formthe final polyamide composition having a final relative viscosityranging from 55 to 200, e.g., from 75 to 200.

Embodiment 32

A process for controlling the caprolactam content of a final polyamidecomposition, the process comprising: (a) providing a base polyamidecomposition having residual caprolactam content greater than 0.6 wt %;(b) determining a desired residual caprolactam content for the finalpolyamide composition; (c) selecting at least one processing conditionfrom catalyst content, delta end group level, temperature, pressure, andmoisture content; and (d) processing the base polyamide compositionunder the at least one condition and based on the desired residualcaprolactam content to form the final polyamide composition having aresidual caprolactam content less than 0.4 wt %.

Embodiment 33

A process for manufacturing a final polyamide composition, the processcomprising: (a) providing a base polyamide composition having one ormore initial properties comprising initial caprolactam content, initialrelative viscosity, and initial color index; (b) determining one or moredesired final properties for the final polyamide composition product,the properties comprising final caprolactam content, final relativeviscosity, and color index; (c) processing the base polyamidecomposition under one or more process conditions comprising catalystcontent, delta end group level, temperature, pressure, and moisturecontent and based on the desired final property to provide the finalpolyamide composition.

While the invention has been described in detail, modifications withinthe spirit and scope of the invention will be readily apparent to thoseof skill in the art. In view of the foregoing discussion, relevantknowledge in the art and references discussed above in connection withthe Background and Detailed Description, the disclosures of which areall incorporated herein by reference. In addition, it should beunderstood that aspects of the invention and portions of variousembodiments and various features recited herein and/or in the appendedclaims may be combined or interchanged either in whole or in part. Inthe foregoing descriptions of the various embodiments, those embodimentswhich refer to another embodiment may be appropriately combined withother embodiments as will be appreciated by one of skill in the art.Furthermore, those of ordinary skill in the art will appreciate that theforegoing description is by way of example only, and is not intended tolimit the invention.

We claim:
 1. A process for producing a polyamide composition having alow residual caprolactam concentration, the process comprising the stepsof: (a) providing a base polyamide composition comprising: a nylonmixture having caprolactam units; from 1 wppb to 50 wppm of a catalystcomposition; and residual caprolactam, and having an initial residualcaprolactam concentration and an initial relative viscosity; (b)processing the base polyamide composition to form the final polyamidecomposition having a final residual caprolactam concentration and afinal relative viscosity.
 2. The process of claim 1, wherein the basepolyamide composition has a delta end group level ranging from 30μeq/gram to 90 μeq/gram.
 3. The process of claim 1, wherein the initialresidual caprolactam concentration is greater than 0.75 wt %, based onthe total weight of the base polyamide composition, and wherein thefinal residual caprolactam concentration is less than 0.75 wt %, basedon the total weight of the final polyamide composition.
 4. The processof claim 1, wherein the final relative viscosity ranges from 40 to 350.5. The process of claim 1, wherein the processing is conducted for abuild time ranging from 2 hours to 30 hours, and a temperature rangingfrom 150° C.-250° C.
 6. The process of claim 1, wherein the finalpolyamide composition has a color index ranging from −6 to 5, asmeasured by ASTM E313 (2018).
 7. The process of claim 1, wherein thefinal relative viscosity is greater than the initial relative viscosity,wherein the final relative viscosity is at least 10% greater than theinitial relative viscosity and the final residual caprolactamconcentration is at least 5% less than the initial residual caprolactamconcentration.
 8. The process of claim 1, wherein the base polyamidecomposition has a melting point ranging from 180° C. to 255° C.
 9. Theprocess of claim 1, wherein the nylon mixture of the base polyamidecomposition comprises: from 1 wt % to 80 wt % nylon-6; and from 20 wt %to 99 wt % nylon-6/6.
 10. The process of claim 1, wherein processingcomprises solid state polymerization, which comprises heating the basepolyamide.
 11. The process of claim 1, wherein the base polyamidecomposition is produced by melt polymerizing a polyamide composition andpelletizing the melted polyamide composition to form polyamide pellets.12. The process of claim 1, wherein the catalyst composition comprisesphosphorous acid; phosphonic acid; alkyl- and aryl-substitutedphosphonic acids; 2-pyridylethyl phosphonic acid; hypophosphorous acid;alkyl-, aryl- and alkyl-/aryl-substituted phosphinic acids; phosphoricacid; esters and salts of these phosphorous-containing acids; manganesehypophosphite; sodium hypophosphite; benzene phosphinic acid; monosodiumphosphate; or any combinations thereof.
 13. The process of claim 1,wherein the base polyamide composition comprises from 0.1 wppm to 35wppm catalyst composition, from 1 wt % to 8 wt % residual caprolactam,has a delta end group level ranging from 50 μeq/gram to 75 μeq/gram, andhas initial relative viscosity less than 35, and wherein the finalpolyamide composition comprises less than 0.6 wt % residual caprolactamand has a final relative viscosity greater than
 45. 14. The process ofclaim 1, wherein the base polyamide composition comprises from 1 wppb to15 wppm phosphorus, greater than 1.5 wt % residual caprolactam, a deltaend group level greater than 50 μeq/gram and has initial relativeviscosity less than 33, wherein the processing is conducted at apressure less than atmospheric pressure and a temperature ranging from175° C. to 185° C., and wherein the final polyamide compositioncomprises less than 0.4 wt % residual caprolactam and has a finalrelative viscosity greater than
 55. 15. The process of claim 1, wherein,during processing, the RV build rate ranges from 1 to 30 RV units/hour.16. A base polyamide composition comprising: a nylon mixture havingcaprolactam units; from 1 wppb to 50 wppm catalyst composition; andgreater than 0.75 wt % residual caprolactam; wherein the base polyamidecomposition has a delta end group level ranging from 30 μeq/gram to 90μeq/gram.
 17. The base polyamide composition of claim 16, wherein thebase polyamide composition has a delta end group level greater than orequal to 45 μeq/gram.
 18. The base polyamide composition of claim 16,wherein the base polyamide comprises greater than 1.4 wt % caprolactamunits, based on the total weight of the base polyamide composition, andwherein the base polyamide has a relative viscosity less than
 55. 19.The base polyamide composition of claim 16, wherein the nylon mixture ofthe base polyamide composition comprises: from 1 wt % to 50 wt %nylon-6; and from 20 wt % to 99 wt % nylon-6/6, wherein the catalystcomposition comprises phosphorous acid; phosphonic acid; alkyl- andaryl-substituted phosphonic acids; 2-pyridylethyl phosphonic acid;hypophosphorous acid; alkyl-, aryl- and alkyl-/aryl-substitutedphosphinic acids; phosphoric acid; esters and salts of thesephosphorous-containing acids; manganese hypophosphite; sodiumhypophosphite; benzene phosphinic acid; monosodium phosphate; or anycombinations thereof.
 20. A film formed from a final polyamidecomposition comprising: polyamide monomers; less than 0.75 wt % residualcaprolactam, wherein the final polyamide composition has a delta endgroup level ranging from 30 μeq/gram to 90 μeq/gram and a melting pointranging from 205° C. to 255° C., wherein the film demonstrates: apuncture resistance greater than 3 J/mm as measured via ASTM F1366(2018), an impact resistance greater than 1500 grams as measured viaASTM D1709. A (2018), and/or a tear resistance greater than 50 grams asmeasured via ASTM D1922 (2018).